(a) Field of the Invention
This invention relates to a method of hydraulic fracturing of an oil and/or gas well bore and more particularly, but not by way of limitation, to a method of creating an effective hydraulic fracture over a selected interval along a length of a well bore. The fracture along the interval encompasses a multitude of oil and/or gas-saturated sand formations and intervening silt and shale formations. The new method of hydraulic fracturing is used for the purpose of more efficiently producing oil and/or gas from all of these formations.
The subject hydraulic fracturing method uses an uncemented, well bore sandpacked annulus to produce a controllable and movable line source of a frac pad fluid injection in a hydraulic fracture, which results in a cylindrical stress field. The stress field is used for propagating the hydraulic fracture. The propagated hydraulic fracture is called herein a “tall frac”. The tall frac is created along a length of the well bore sandpacked annulus.
(b) Discussion of Prior Art
Heretofore in the oil and gas industry, hydraulic fracturing of a well bore involved injecting frac pad fluids through selected perforations in a well casing surrounded by a cement-filled annulus. The objective was to provide adequate isolation of each targeted oil and gas reservoir zone, by carefully cementing the annulus space so that the injected frac pad fluid would create a fracture only in the perforated reservoir zone and would not grow either upward or downward across shale barriers into adjacent zones. Using a limited entry technique, two, three, or more zones within a relatively short interval are perforated and simultaneously frac treated. In some cases, the fracture propagating outward from each perforated zone may interconnect with each other across lithologic barriers, or alternatively, each perforated zone may propagate a separate, isolated, hydraulic fracture without communication through the intervening barriers.
Also, multistage frac programs have been developed to achieve hydraulic fractures in a multiplicity of separated sand packages spaced over extended intervals along the length of the well bore. However, each stage of this type of multistage frac program has to be separately isolated, perforated, and frac-pumped, thereby requiring extended periods of time with large, repetitive, frac-treatment costs.
The above described hydraulic fractures are created essentially by point source fluid injection, resulting in spherical stress fields created around each of the point sources. The resulting hydraulic fracture, created by the spherical stress field, is propagated from each such point source in a plane perpendicular to the direction of the least principal stress in the formation rock with no dimensional restraints.